Stirling engines are classified roughly into those of four groups shown in FIGS. 7A to 7D.
(1) An α-type Stirling engine shown in FIG. 7A has a series assembly of a heater H, a regenerative heat exchanger R and a cooler C arranged in that order, two cylinders S1 and S2, and power cylinders PP1 and PP2 slidably fitted in the cylinders S1 and S2, respectively. The series assembly of the heater H, the regenerative heat exchanger R and the cooler C is connected to top spaces in the cylinders S1 and S2.
(2) A β-type Stirling engine shown in FIG. 7B has a cylinder S, a displacer piston DP fitted in the cylinder S, a power piston PP connected in series to the displacer piston DP and fitted in the cylinder S, and a series assembly of a heater H, a regenerative heat exchanger R and a cooler C arranged in that order. The series assembly of the heater H, the regenerative heat exchanger R and the cooler C is connected to a space SA extending above the displacer piston DP in the cylinder S and a space SB extending under the displacer piston DP. The space SA and the space SB communicate with each other by means of the series assembly of the heater H, the regenerative heat exchanger R and the cooler C.
(3) A γ-type Stirling engine shown in FIG. 7C has a displacer cylinder DS, a displacer piston DP fitted in the displacer cylinder DS and defining space. DSA and DSB in the displacer cylinder DS, a power cylinder PS, a power piston PP fitted in the power cylinder PS and defining a space DSA in the power cylinder PS, and a series assembly of a heater H, a regenerative heat exchanger R and a cooler C. The series assembly of the heater H, the regenerative heat exchanger R and the cooler C is connected to the two spaces DSA and DSB. The space DSB in the cylinder DS and the space PSA in the cylinder PS communicate with each other.
(4) A double-acting Stirling engine shown in FIG. 7D has four staggered cylinders S1, S2, S3 and S4, four series assemblies each of a heater H, a regenerative heat exchanger R and a cooler C, rotating swash plates, not shown, placed in middle parts of the cylinders S1, S2, S3 and S4, respectively, and power pistons PP1, PP2, PP3 and PP4 placed in the cylinders S1, S2, S3 and S4 and interlocked with the swash plates, respectively. Each series assembly of the heater H, the regenerative heat exchanger R and the cooler C is connected to a top space SA in one of the adjacent cylinders and a bottom space SB in the other cylinder.
A waste heat utilizing system disclosed in JP 1-294946 A includes a water-cooled internal combustion engine and two β-type Stirling engines combined with the water-cooled internal combustion engine. One of the two β-type Stirling engines operates on heat provided by cooling water for cooling the water-cooled internal combustion engine and the other β-type Stirling engine operates on heat provided by an exhaust gas discharged from the water-cooled internal combustion engine.
This known waste heat utilizing system using the cooling water and the exhaust gas as heat sources for the two β-type Stirling engines needs complicated piping having high sealing effect. Therefore, it is difficult to form the waste heat utilizing system in small, lightweight construction at a low cost.
Although the waste heat utilizing system is provided with the two β-type Stirling engines, the output and efficiency were low because one of the β-type Stirling engines uses, as a heat source, the cooling water of a temperature on the order of 100° C. lower than that of the exhaust gas.
The present invention has been made to overcome those difficulties and it is therefore an object of the present invention to provide a low-cost, lightweight, compact, reliable multistage Stirling engine and capable of generating a high output at a high efficiency.